The field of invention is adjustable guitar structures and their construction as well as methods to accurately intonate acoustic guitars.
The six-string acoustic guitar has survived many centuries without much alteration to its original design. Prior to the present invention, one very important aspect of acoustic guitars that has been overlooked is providing proper intonation of each string--which is defined as adjusting the saddle longitudinally with the string until all of the notes on the instrument are relatively in tune with each other. Traditional methods of acoustic guitar construction intonate the high and low E strings which are connected to the bridge with a straight non-adjusting saddle. The other four strings are either close to being intonated or, as in most cases, quite a bit out of intonation. Historically, discrepancies in intonation were simply accepted by the artist and the general public as it was not believed that perfect or proper intonation on an acoustic guitar was attainable. The artist accepted this fact by playing out of tune in various positions on the guitar, or developed a compensating playing technique to bend the strings to pitch while playing; which was difficult and/or impossible to do.
Especially in a studio setting, the acoustic guitar must play in tune with more precisely intonated instruments and the professional guitarist cannot have an acoustic guitar that is even slightly off in intonation.
If, for example, the weather or temperature changes, the guitar string gauge is changed, string action (height) is raised or lowered, the guitar is refretted, or a number of any other conditions change, the guitar must be re-intonated. This especially plagues professional musicians who frequently travel or tour giving concerts around the country in different climatic zones, which cause guitars to de-tune and require adjustability in intonation. Airplane travel, with the guitar being subjected to changes in altitude and pressures, exacerbates these problems. Accordingly, adjustability of intonation is desirable due to the many factors which seriously effect the acoustic guitar. Yet, most acoustic guitar companies still use the original non-adjustable single saddle. The fully adjustable acoustic guitar bridge claimed herein is the only system known to the inventors that allows for continuous fully adjustable intonation of each string without sacrificing the sound of the instrument. Thus, there has been a need for the improved construction of adjustable intonation apparatus and methods to properly intonate acoustic guitars.
Attempts to properly intonate acoustic guitars have been made without success. In the 1960's, attempts were made by Gibson.RTM. with the Dove.RTM. acoustic guitar by putting a so called Nashville Tune-O-Matic bridge.RTM. on the acoustic guitar. The Tune-O-Matic was designed for electric guitars and although it theoretically allowed the acoustic guitar to be intonated, the electric guitar metal bridge destroyed the acoustic tone and qualities of the acoustic guitar. Accordingly, these guitars were believed to have been discontinued, or have not been accepted in the market, at least by professional guitar players. In the 1970's, a compensated acoustic guitar bridge was developed which cut the saddle into two or three sections and intonated the guitar strings individually with two, three, or four strings on each saddle. This method however is not individually and continuously adjustable and thus has the major drawbacks listed above. It is important to note that traditional electric guitar bridges either have an adjustment screw running through the metal saddle, with the screw connected at both ends of the bridge (Gibson Tune-O-Matic), or springs loaded on the screw between the saddle and the bridge to help stabilize the saddle (as on a Stratocaster electric guitar). The above construction is not adaptable to acoustic guitars. On an acoustic guitar, if either the screw is connected at both ends of the bridge, or a spring is placed between the saddle and the screw, the saddle will be restricted in its vibration, thereby choking off or dampening the string vibration, resulting in lack of sustain (duration of the note's sound), no tone, or acoustic quality.
Other reasons why electric guitar bridges are not transferrable to acoustic guitars is that electric guitar bridges are constructed of metal which produces a bright tone with the electric guitar strings (wound steel as opposed to the acoustic guitar's wound phosphor bronze strings or nylon). The saddles on an electric guitar bridge are fixed (springs or the adjustment bolt connected at both ends of the bridge) since the pickups (guitar microphones) are located between the bridge and the neck and the electric guitar does not rely on an acoustic soundboard to project the sound. The electric guitar strings simply vibrate between two points and the vibrations are picked up by the electric guitar pickups.
The saddles for the acoustic guitar bridge cannot be made of metal (steel, brass, etc.). The acoustic guitar relies on the string vibrations to be transmitted from the saddles to the base of the bridge. The vibrations go from the bridge to the guitar top (soundboard) and on acoustic/electric guitars to the pickups; either internal under the bridge and/or connected against the soundboard to pickup the soundboard's vibrations. The saddle must be constructed of an acoustically resonant material (bone, phenolic, ivory, etc.) to be able to transmit the string vibrations to the base of the bridge. Metal saddles would dampen these vibrations and the acoustic guitar would produce a thin, brittle tone with very little or no sustain of the notes being played.
The claimed invention solves these problems. The saddle capture has a slight bit of slop or looseness in its threading with the adjustment bolt. Indeed, while round holes with clearance will work, the preferred hole is oval allowing maximum up and down freedom of movement. The saddle must have this small bit of freedom to vibrate in order to transmit the string vibrations into clear, full bodied, warm toned notes that will ring and sustain through the projection of the acoustic guitar's soundboard and/or internal pickups.
Another aspect of the present invention relates to making adjustments to the so-called Rule of 18. Standard guitars are manufactured using a mathematical formula called the Rule of 18 which is used to determine the position of the frets. A short explanation of the acoustic guitar is helpful to understanding this.
The acoustic guitar includes six strings tuned to E, A, D, G, B, and E from the low to high strings. Metal strips running perpendicular to the strings called frets 20, allow for other notes and chords to be played. (See FIGS. 1-4.) The positioning of the frets are determined by employing the Pythagorean Scale. The Pythagorean Scale is based upon the following consonant interval ratios: the fourth, the fifth, and the octave. As shown in FIG. 3, Pythagoras used a movable bridge 50 as a basis, to divide the string into two segments at these ratios. This is similar to the guitar player's finger pressing the guitar string down at selected fret locations between the bridge and the nut (FIG. 4).
To determine fret positions, guitar builders use a mathematical formula based from the work of Pythagoras called the Rule of 18 (the number used is actually 17.817). The guitar scale length is divided by 17.817. This is the distance from the nut (see FIG. 5) to the first fret. The remaining scale length is divided by 17.817 to determine the second fret location. This procedure is repeated for all of the fret locations up the guitar neck. For example, focusing on FIGS. 5A and 5B, in an acoustic guitar with a scale length of 25.5", the following calculations are appropriate:
______________________________________ 25.5 .div. 17.817 = 1.431" (a) distance from nut to first fret 25.5 - 1.431 = 24.069" 24.069 .div. 17.817 = 1.351" (b) distance between first and second fret or 1.431 + 1.351 = 2.782" distance from nut to second fret ______________________________________
The procedure and calculations continue until the required number of frets are located. Some altering of numbers is required to arrive at having the twelfth fret location exactly at the center of the scale length and the seventh fret producing a two-thirds ratio for the fifth interval, etc.
Unfortunately, this system is inherently deficient in that it does not result in perfect intonation. As one author stated: "Indeed, you can drive yourself batty trying to make the intonation perfect at every single fret. It'll simply never happen. Why? Remember what we said about the Rule of 18 and the fudging that goes on to make fret replacement come out right? That's why. Frets, by definition, are a bit of compromise, Roger Sadowsky observes. Even assuming you have your instrument professionally intonated and as perfect as it can be, your first three frets will always be a little sharp. The middle register--the 4th through the 10th frets--tends to be a little flat. The octave area tends to be accurate and the upper register tends to be either flat or sharp; your ear really can't tell the difference. That's normal for a perfectly intonated guitar." (See The Whole Guitar Book, "The Big Setup," Alan di Perna p.17, Musician 1990.
While this prior art system is flawed, prior to this invention it was just an accepted fact that these are the best results that guitar makers have come up with.